Grease composition

ABSTRACT

A grease composition includes: at least one mineral-based, synthetic-based, or natural-based oil, a thickener predominantly consisting of at least one simple or complex aluminium soap; at least one molybdenum dithiocarbamate; and graphite. The grease can be used for the lubrication of open systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Entry of International ApplicationNo. PCT/IB2011/055622, filed on Dec. 12, 2011, which claims priority toFrench Patent Application Serial No. 1060442, filed on Dec. 13, 2010,both of which are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to grease compositions which can be usedin particular in industrial applications or public works, requiring verygood resistance to high loads and impacts.

BACKGROUND

There are numerous applications where liquid lubricants are unsuitablebecause they “drift” with respect to the lubrication point. These are inparticular rolling-contact bearings and slider bearings, open gear sets,metal cables and chain drives, and more generally applications with nosealing system. For these applications, lubricating greases are used,which are solid or semi-fluid substances resulting from the dispersionof a thickener in a liquid lubricant, incorporating additives whichconfer particular properties upon them.

The vast majority of lubricating greases are prepared with thickeners offatty acid metal salt types. The fatty acid is dissolved in the base oilat a relatively high temperature, and then the appropriate metalhydroxide is added. After having evaporated by boiling the water formedduring the reaction, cooling is carried out for a specific period oftime in order to form the soap lattice.

Lithium, sodium, calcium, barium, titanium or aluminium hydroxides, orcertain aluminium trimers, are suitable for example as metal compoundsfor manufacturing grease. Long-chain fatty acids, of the order of C14 toC28, mainly C18, generally originate from vegetable (castor oil forexample), or animal (for example tallow) oils. They can be hydrogenated.The best-known derivative is 12-hydroxystearic acid originating fromricinoleic acid. In combination with the long-chain fatty acids, it isalso possible to use short-chain acids, typically comprising between 6and 12 carbon atoms, such as for example azelaic acid, benzoic acid.So-called complex greases are then formed.

The metal soaps form a fibrous structure, except for the aluminiumsoaps, which exhibit a spherical gel structure. Other inorganicthickeners such as, for example, bentonite, silica gel can be used. Thethickeners also include polycarbamides (polyureas). For applicationswhere the grease is located in an unconfined enclosure (for example opengear sets in cement works etc.), greases thickened with metal soaps, andin particular with simple or complex metal soaps of aluminium aregreatly superior to the other greases.

In fact, the greases thickened with polyureas do not have sufficientmechanical stability, in particular due to their thixotropic nature,which leads to their becoming destructured under mechanical stresses.The inorganic thickeners also present problems of mechanical resistanceand water resistance, which has a detrimental effect in open systems.

As for the metal soaps, they exhibit very good mechanical resistance. Inparticular, the greases thickened with simple or complex aluminium soapsexhibit very good mechanical resistance, are highly water-resistant (inparticular the complex aluminium greases), and exhibit excellentadhesion to metal surfaces.

Patent FR 1 048 670 describes for example a grease comprising analuminium soap, allowing the lubrication of heavy parts in industry,which operate under stringent temperature and load conditions. Thepresence of aluminium soap prevents the separation of the base oil fromthe grease, and therefore the destructuring of the grease. ApplicationFR 2 172 080 also describes particularly stable greases thickened withaluminium soaps, as does application FR 2 012 238, which also stressestheir water resistance.

Application EP 0661378 discloses examples of greases thickened withcomplex aluminium soaps containing molybdenum dithiocarbamate (MoDTC),alone or in combination with zinc dithiophosphate (ZnDTP). Thesecompositions contain no graphite. Their EP performances are mediocre,particularly those of the grease containing only MoDTC.

Greases thickened with complex aluminium soaps, and comprisinganti-wear, extreme pressure additives, as well as a friction modifier,molybdenum bisulphide (MoS2), are marketed under the name of COPAL MS 2for application to open gear sets in heavy industry such as the cementindustry, in sugar refineries (grinding mills, kiln girth gear drives,stewing rings), or for heavy construction machinery. The presence ofMoS2 guarantees good lubrication even in the event of accidentaloverheating and avoids any binding or jamming of the lubricatedcomponents. However, these greases have a high molybdenum (Mo) content,that it would be useful to reduce for environmental reasons, andextreme-pressure properties which could be improved, in particular inorder to withstand impacts and jolts, for example in grinding mills andheavy-construction machinery. The greases can contain various solidlubricants, known for their friction properties and their anti-wearproperties, such as for example molybdenum or tungsten bisulphide,graphite or polytetrafluoroethylene (PTFE).

Application FR 2 723 747 discloses high-temperature greases forconstant-velocity joints comprising mineral and/or synthetic base oils,polyurea thickeners and MoS2 as solid lubricant, as well as graphite andat least one organic molybdenum compound, preferentially molybdenumdithiocarbamate. The solid lubricants graphite, MoDTC, PTFE, make itpossible to reduce the content of expensive solid lubricant MoS2, butwithout however replacing it completely. The molybdenum content of thecompositions disclosed is at least of the order of 5000 ppm.

This application does not relate to the field of greases for opensystems, in industry or in public works, and does not describe greasesthickened with simple or complex aluminium soaps. The problem is toproduce greases for vehicle constant-velocity joints withhigh-temperature resistance, and having an improved lifespan, lubricity,and constant load resistance. No mention is made of the improvement inthe extreme-pressure properties.

The publication “Effect of graphite on friction and wear characteristicsof molybdenum dithiocarbamate”, Y. Yamamoto et al., Tribology Letters,Vol 17, No. 1, July 2004, discloses the booster effect of graphite onthe anti-wear and friction performances of MoDTC, in a specificlubricating oil, squalane. This improvement does not relate to theextreme-pressure properties, and is especially appreciable in thepresence of succinimide dispersant. This study is limited to a singlenatural lubricating oil and does not deal with the field of greases. Nospecific combination of base oil, graphite and MoDTC with othercomponents necessary for the formulation of greases, in particularthickeners, is disclosed. It is therefore absolutely impossible toconclude from this publication whether the booster effect of thegraphite on the friction and wear performances of the MoDTC, and evenless on the extreme-pressure properties, will be reproduced in a greasecomprising a particular thickener.

Surprisingly, the applicant found that greases thickened with aluminiumsoaps, and comprising, as friction modifier, a molybdenumdithiocarbamate combined with graphite, exhibited improvedextreme-pressure properties. The compositions according to the inventioncan exhibit these improved properties with a reduced molybdenum content.

SUMMARY

The present invention relates to grease compositions comprising:

-   -   (a) one or more base oils of mineral, synthetic or natural        origin,    -   (b) a thickener composed predominantly of one or more simple or        complex aluminium soaps,    -   (c) one or more molybdenum dithiocarbamates,    -   (d) graphite.

Preferentially, the compositions according to the invention comprise, asbase oils (a), one or more mineral base oils, alone or in a mixture, andoptionally one or more synthetic base oils. According to an embodiment,the compositions according to the invention comprise at least onecomplex aluminium soap as thickener (b). Preferentially, in thecompositions according to the invention, the simple or complex aluminiumsoap(s) constitute at least 80% by weight of the thickener (b) in saidcompositions.

According to an embodiment, the grease compositions according to theinvention also comprise one or more additives chosen from the anti-wearand/or extreme-pressure additives, preferentially containing phosphorusand sulphur, preferentially the dithiophosphates. According to apreferred embodiment, the compositions according to one of claims 1 to 5comprise moreover one or more polymers, preferentially chosen from thepolyisobutenes. Preferentially, in the compositions according to theinvention, the molybdenum content is comprised between 500 and 5000 ppm,preferentially between 1000 and 4800 ppm.

Preferentially, in the compositions according to the invention, thecontent by mass of graphite is comprised between 0.5 and 3%,preferentially between 0.7 and 2%.

The present invention also relates to the use of a grease composition asdescribed above for the lubrication of open systems, preferentially opengear sets, metal cables, chain drives. Preferentially, this use takesplace in the field of industry, preferentially the cement, sugar orsteel industry, or in the field of public works. The present inventionalso relates to the use of an additive composition comprising molybdenumdithiocarbamate and graphite in order to increase the welding load,measured according to the standard DIN 51350/4, of a grease thickenedwith simple or complex aluminium soaps. Finally, the present inventionalso relates to an open system, preferentially open gear sets, metalcable, chain drive, to which a grease composition as described above isapplied.

DETAILED DESCRIPTION Lubricating Base Oils (a)

The or the base oil(s) used in the compositions according to the presentinvention can be oils of mineral or synthetic origin of Groups I to Vaccording to the classes defined in the API (American PetroleumInstitute) classification. The mineral base oils according to theinvention include all types of bases obtained by atmospheric and vacuumdistillation of crude oil, followed by refining operations such asextraction with a solvent, deasphalting, dewaxing with a solvent,hydrotreatment, hydrocracking and hydroisomerization, hydrofinishing.The base oils of the grease compositions according to the presentinvention can also be synthetic oils, such as certain esters, silicones,glycols, polybutene, polyalphaolefins (PAO), alkylbenzene,alkylnaphthalene. The base oils can also be oils of natural origin, forexample alcohol and carboxylic acid esters, which can be obtained fromnatural resources such as sunflower, rapeseed, palm, soya oil etc.

According to an embodiment, the grease compositions according to theinvention contain a mixture of mineral oils, for example paraffinicmineral oils and naphthenic mineral oils, as base oils (a). According toanother embodiment, they contain a mixture of mineral oil(s), forexample paraffinic mineral oils and naphthenic mineral oils, and ofsynthetic oils, for example polyalphaolefins. The mixture of base oils(a) is set so that its viscosity at 40° C. according to the standardASTM D 445 is comprised between 100 and 500 cSt, preferentially between110 and 300 cSt, preferentially between 150 and 250 cSt.

Thickeners (b)

The greases according to the present invention are thickened with simpleor complex aluminium soaps which exhibit superior mechanical propertiesand adhesion to surfaces, as well as excellent water resistance. Thealuminium and fatty acid soaps can be prepared separately, or in situduring the manufacture of the grease (in the latter case, the fattyacid(s) are dissolved in the base oil, then the appropriate metalcompound is added). The simple aluminium soaps are for example preparedfrom aluminium hydroxide Al(OH)3 and one or more long-chain fatty acids,typically comprising from 10 to 28 carbon atoms, saturated orunsaturated, for example stearic acid.

The complex aluminium soaps are for example prepared from stearic acid,benzoic acid, and aluminium trimers corresponding to formula (I):

Where R is a hydrocarbon radical, preferentially alkyl, for exampleisopropyl.

Compared with the simple soaps, the complex aluminium soaps have theadvantage of a better high-temperature performance. The aluminium soapsare preferentially used in contents of the order of from 5 to 30% byweight, preferentially from 10 to 25% by weight, preferentially from 105to 20% by weight, typically 12% by weight in the greases according tothe invention. In the compositions according to the invention, thequantity of metal soap(s) is generally adjusted so as to obtain greasesof grade 00, of grade 0, of grade 1 or of grade 2 according to the NLGIclassification.

The greases according to the invention mainly contain simple or complexaluminium soaps as thickener. This means that these soaps togetherrepresent the highest percentage by weight in the greases according tothe invention, compared with the percentage by weight of the otherthickening materials. Preferentially, the quantity of the simple orcomplex aluminium soap(s), constitutes at least 50%, even morepreferentially at least 80% by weight with respect to the total weightof thickening materials, in the grease compositions according to theinvention.

According to an embodiment, the greases according to the invention cancontain simple or complex metal soaps of fatty acids as the mainthickener, and smaller quantities of other thickeners, such as othersimple or complex metal soaps, polyureas, or inorganic thickeners, ofthe bentonite or aluminosilicate type. Preferentially, the greasesaccording to the invention are free of polyurea-type thickeners, whichare technically more complicated to manufacture, in particular becausethe components used in their manufacture, such as the isocyanates andamines, are very toxic and not very stable during storage. Even morepreferentially, the greases according to the invention exclusivelycontain simple or complex metal soaps of aluminium as thickener.

Molybdenum Dithiocarbamate and Graphite

The grease compositions according to the invention contain graphite andmolybdenum dithiocarbamate. It was surprisingly found, even thoughgraphite is known for its low resistance under a high load, that thiscombination makes it possible to obtain greases thickened with aluminiumsoaps having very good extreme-pressure properties, with a reduced levelof molybdenum. It is not desirable to completely remove the molybdenumcompounds as the greases thickened with aluminium soaps which containnone, or few, of these show no improvement in extreme-pressureproperties. For example, graphite is known to present problems ofresistance under a high load, and a grease containing only graphite hasmediocre extreme-pressure properties.

Moreover, the greases containing only molybdenum dithiocarbamate asadditives do not guarantee adequate protection of parts because MoDTCrequires a certain activation temperature in order to be effective, andit is generally used in combination with other additives, in particularadditives containing phosphorus and sulphur. The greases thickened withaluminium soaps (complex) containing only MoDTC as additive havemediocre extreme-pressure performances.

Molybdenum Dithiocarbamate (MoDTC) (c)

The compositions according to the invention contain molybdenumdithiocarbamates, friction-modifying additives well known to a personskilled in the art. These molybdenum dithiocarbamate organometallicfriction modifiers can for example be molybdenum dialkyldithiocarbamatescorresponding to formula (II):

Where X₁, X₂, X₃, X₄ are alkyl chains, preferentially comprising from 2to 13 carbon atoms, preferentially from 2 to 6 carbon atoms.

Preferentially, the quantity of MoDTC in the compositions according tothe invention is adjusted so that their molybdenum content is comprisedbetween 500 and 5000, preferentially between 1000 and 4800 ppm,preferentially between 1500 and 4500 ppm, preferentially between 2000and 4000, preferentially between 2500 and 3000 ppm. Too low an MoDTCcontent leads to mediocre extreme-pressure properties, too high acontent is damaging to the environment. This content can be measuredaccording to the usual techniques, plasma, atomic absorption, X-rayfluorescence.

Typically, the content by mass of dialkyldithiocarbamate of thecompositions according to the invention is comprised between 0.3 and 2%,preferentially between 0.5 and 1.7%, preferentially between 0.7 and1.5%, preferentially between 0.8 and 1.2%, typically equal to 1%.According to a preferred embodiment, in the compositions according tothe invention, the Mo/[graphite] ratio between the molybdenum content,in ppm, and the percentage by mass of graphite in said compositions, iscomprised between 1000 and 4000, preferentially between 1500 and 3500,preferentially between 2000 and 3000, preferentially between 2500 and2900. This Mo/[graphite] ratio allows an optimization of theextreme-pressure properties for a given quantity of MoDTC.

Graphite (d)

The grease compositions according to the invention contain graphite, inany form that can be incorporated in the greases. For example, thegraphite used in the compositions according to the invention can be apowder of micrometric size, with particle sizes comprised approximatelybetween 1 and 15 μm, and for example a size distribution characterizedby a diameter D50 comprised between 3 and 8 μm, preferentially between 5and 7 μm. Preferentially, the content by mass of graphite in thecompositions according to the invention is comprised between 0.5 and 3%,preferentially between 0.7 and 2%, preferentially between 0.8 and 1.5%,preferentially between 0.9 and 1.2%.

Anti-Wear and Extreme Pressure

The greases according to the invention optionally contain anti-wear andextreme-pressure additives containing phosphorus and sulphur, commonlyused in the formulation of greases and lubricants. These are for exampleand non-limitatively thiophosphoric acid, thiophosphorous acid, theesters of these acids, the salts thereof and the dithiophosphates,preferentially the dithiophosphates, in particular zinc dithiophosphates(ZnDTP).

The zinc dithiophosphates of formula (III) are in particular preferred:

whereR₁, R₂, R₃, R₄ are, independently of each other, linear or branchedalkyl groups comprising from 1 to 24, preferentially from 3 to 14 carbonatoms or optionally substituted aryl groups comprising from 6 to 30,preferentially from 8 to 18 carbon atoms.

These different compounds can be used alone or in a mixture in thegrease compositions according to the invention. Their percentage by massis preferentially comprised between 0.5 and 5% by weight, preferentiallybetween 0.7 and 2% by weight, or also between 0.8 and 1.5% by weightwith respect to the total weight of the composition. The lubricatingcompositions according to the present invention can also containphosphorus-containing anti-wear and extreme-pressure additives, such asfor example the alkyl phosphates or alkyl phosphonates, phosphoric acid,phosphorous acid, the mono, di and triesters of phosphorous acid andphosphoric acid, and salts thereof. The lubricating compositionsaccording to the present invention can also contain sulphur-containinganti-wear and extreme-pressure additives, for example thedithiocarbamates, thiadiazoles and benzothiazoles, sulphurized olefins.

Other Additives

The greases according to the invention can also contain any types ofadditives suited to their use, for example antioxidants, such asaminated or phenolic antioxidants, anti-rust additives which can beoxygenated compounds such as esters, for example sorbitan monoleate,oxidized waxes, copper passivators etc. These different compounds aregenerally present in contents less than 1%, or even 0.5% by mass in thegreases.

The greases according to the invention can also contain polymers, forexample polyolefins, polyisobutene (PIB), polyethylenes, polypropylene,heavy PAOs, olefin copolymers (OCP) for example hydrogenateddiene/styrene, polymethacrylates (PMA), in contents generally comprisedbetween 1 and 35%. These polymers are used to improve the cohesivenessof the greases, which thus withstand centrifugation better. Thesepolymers (in particular the PIBs) also result in better adhesion of thegrease to surfaces, and increase the viscosity of the base oil fractionand therefore the thickness of the film of oil between parts subject tofriction. The quantity incorporated varies as a function of the molarmass, viscosity, and sought effect. For example, PIBs with a molar masscomprised between 15,000 and 25,000 daltons at contents comprisedbetween 1 and 10% by mass, are used in order to increase the adhesion ofthe grease to the metal surfaces.

Method for Preparing the Greases

The greases according to the invention are preferentially manufacturedby forming the metallic soap in situ. One or more fatty acids aredissolved in a fraction of the base oil or the base oil mixture at roomtemperature. This fraction is generally of the order of 50% of the totalquantity of oil contained in the final grease. The fatty acids can belong acids, comprising from 14 to 28 carbon atoms, in order to form asimple soap, optionally combined with short fatty acids, comprising from6 to 12 carbon atoms, in order to form complex soaps.

The compounds containing aluminium, preferentially of the aluminiumtrimer type as described above, are added at a temperature ofapproximately 60 to 80° C. The reaction of the fatty acids with thealuminium-containing compound(s) is allowed to proceed while heating toapproximately 200° C. The grease is then cooled down, in particular bythe remaining base oil fraction. The additives are then incorporated atapproximately 80° C. followed by mixing for a sufficient time to obtaina homogeneous grease composition.

Grade of the Greases

The consistency of a grease measures its hardness or its fluidity atrest. It is quantified by the penetration depth of a cone with givendimensions and mass. The grease is subjected to mixing beforehand. Theconditions for measuring the consistency of a grease are defined by thestandard ASTM D 217.

According to their consistency, the greases are divided into 9 NLGI(National Lubricating Grease Institute) classes or grades commonly usedin the field of greases. These grades are shown in the table below. Thegreases according to the invention are preferentially greases ofconsistency comprised between and 265 and 430, preferentially between310 and 430, preferentially between 265 and 340 tenths of a millimetreaccording to ASTM D217. Preferentially, they are of grade NLGI 00, 0, 1or 2, i.e. their consistency is respectively comprised between 400 and430, or 355 and 385, or 310 and 340, or 265 and 295 tenths of amillimetre according to ASTM D217.

The greases intended for open gear sets must adhere to the surfaces, butshould not be too consistent as they are applied by bubbling of thegears in a tank or by spraying. The grades 0, 00, or 1 are thereforepreferred, i.e. greases with a consistency respectively comprisedbetween 400 and 430, or 355 and 385, or 310 and 340 tenths of amillimetre according to ASTM D217.

Grade of the greases Consistency according to ASTM D NLGI grade 217(tenths of a millimetre) 000 445-475 00 400-430 0 355-385 1 310-340 2265-295 3 220-250 4 175-205 5 130-160 6  85-115

Example 1

Grease compositions were prepared with a base grease prepared from basemineral oil, and a complex aluminium soap obtained by the reaction ofbenzoic acid, glycerol tristearate (stearin), and a source of aluminium(aluminium trimer corresponding to formula (I) above). The base oilrepresents 82.50% by weight of the base grease, and the complexaluminium soap 17.50% by weight.

These are grade 2 greases according to the NLGI classification.

This base grease is used in the composition of a commercial greasecomprising 2.5% MoS2, and various additives: an anti-wear additive(ZnDTP), an extreme pressure additive as well as an anti-rust additive,which is taken as reference (reference 1). The grease compositions wereprepared with the same base grease and with the same additives as thecommercial reference grease, but with the MoS2 completely or partiallyreplaced by other solid lubricants:

-   -   The graphite used is a micrometric powder, of diameter D50=6 μm    -   The MoDTC used is di-n butyl molybdenum dithiocarbamate,        containing 28% by mass molybdenum    -   The MoS₂ used is a micrometric powder constituted by particles        with a size comprised between 0.5 and 8 μm, of D50 approximately        2 μm.

The extreme-pressure performances of all these greases were measuredaccording to the standard DIN 51350/4, by measuring the welding load inthe 4 ball EP test (measurement of the load that needs to be applied inorder to weld together 4 balls arranged according to a specificarrangement and between which a specific quantity of grease has beenintroduced). Table 1 summarizes the compositions and performances ofgreases A to E in comparison with reference 1. The greases D and Eaccording to the invention have significantly improved extreme-pressureproperties (EP) compared with the reference, and a much lower molybdenumcontent. Grease A, which contains no molybdenum, shows no improvement inthe extreme-pressure properties. Greases B and C show a slightimprovement in the EP properties (less than that observed with greases Dand E), but their molybdenum content remains very high.

Example 2

Grease compositions were prepared with a base grease prepared frommineral base oil, and a simple lithium soap obtained by reaction of12-hydroxystearic acid and lithium hydroxide (LiOH, H2O) The base oilrepresents 90.00% by weight of the base grease, and the simple lithiumsoap 10.00% by weight. These are grade 2 greases according to the NLGIclassification.

This base grease is used in the composition of a grease taken asreference (reference 2) comprising moreover 1% MoS2, and variousadditives: an anti-wear additive (ZnDTP), an extreme pressure additive,as well as an anti-rust additive, which is taken as reference (reference2). Grease compositions F and G were prepared with the same base greaseand the same additives as the reference 2 grease, but the MoS2 wasreplaced by graphite and MoDTC (identical to those of example 1). Theextreme pressure performances of the reference 2 grease and greases Fand G were measured according to the standard DIN 51350/4, by measuringthe welding load in the 4 ball EP test.

Table 1 summarizes the compositions and the performances of greases Fand G in comparison with reference 2 grease. No improvement in theextreme-pressure properties was found between reference 2 grease andgrease F or grease G. In this context of thickening with lithium soap,the combination of MoDTC+graphite does not act in the same way as in thecontext of thickening with aluminium.

Without wishing to be bound by any theory, it seems that the sphericalgel structure of the aluminium soaps, which is distinguished from thefibrous structure of the other metal soaps of fatty acids (in particularlithium), used as thickeners, has an influence on the mode of action andthe performances of the additives.

TABLE 1 Reference 1 A B C D E Reference 2 F G % by base grease 89.6089.10 88.10 89.10 89.10 90.10 91.50 91.50 91.00 mass MoS2 2.50 2.00 1.001.00 PTFE 2.00 2.00 MoDTC 1.50 1.00 0.50 1.00 Graphite 1.00 2.00 1.501.00 0.50 0.50 Additives 7.90 7.90 7.90 7.90 7.90 7.90 7.50 7.50 7.50Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Mo content(ppm) 15000 0 12000 6000 4200 2800 6000 1400 2800 4 balls EP DIN 51350/4improvement/reference 0% 10% 20% 70% 80% 0% 0%

1.-12. (canceled)
 13. A grease composition comprising: (a) one or morebase oils of mineral, synthetic or natural origin; (b) a thickenercomprising mainly of one or more simple or complex aluminium soaps; (c)one or more molybdenum dithiocarbamates; and (d) Graphite.
 14. Thegrease composition according to claim 13 comprising as base oils (a) oneor more mineral base oils, alone or in a mixture.
 15. The greasecomposition according to claim 13 comprising at least one complexaluminium soap as thickener (b).
 16. The grease composition according toclaim 13 where the simple or complex aluminium soap(s) constitutes atleast 80% by weight of the thickener (b) in the composition.
 17. Thegrease composition according to claim 13 comprising at least oneadditive chosen from: anti-wear and extreme pressure additives.
 18. Thegrease composition according to claim 13 comprising at least onepolymer.
 19. The grease composition according to claim 13 in which themolybdenum content is comprised between 500 and 5000 ppm.
 20. The greasecomposition according to claim 13 wherein the content by mass of thegraphite is comprised between 0.5 and 3%.
 21. A method for lubricatingopen systems, wherein the open systems are brought into contact with agrease composition comprising: (a) one or more base oils of mineral,synthetic or natural origin; (b) a thickener comprising mainly of one ormore simple or complex aluminium soaps; (c) one or more molybdenumdithiocarbamates; and (d) Graphite.
 22. The method according to claim21, wherein the open systems are used in the field of at least one of:industry or public works.
 23. An open mechanical movement system towhich a grease composition is applied, the grease compositioncomprising: (a) one or more base oils of mineral, synthetic or naturalorigin; (b) a thickener comprising mainly of one or more simple orcomplex aluminium soaps; (c) one or more molybdenum dithiocarbamates;and (d) Graphite.
 24. The open mechanical movement system of claim 23,further comprising at least one of the following unsealed components towhich the grease composition is applied: (a) bearings; (b) gears; (c)cables; and (d) chains.